To meet the demand for continuously increasing data rates in wireless communication, radio frequency spectrum and spectral efficiency are increased. For example, areal spectral efficiency has to be increased as the density of wirelessly connected devices increases, which includes both user devices and autonomous devices.
3GPP Long Term Evolution (LTE) has been developed for spectral efficiency. Its initial deployment was limited to licensed spectrum. One of the main work items for Release 13 and future releases of LTE is License-Assisted Access (LTE-LAA), which additionally uses unlicensed spectrum (e.g., at 2.4 GHz and 5.1 GHz) for LTE or LTE-like transmission in coexistence with other wireless standards such as a Wireless Local Area Network (WLAN or Wi-Fi) according to IEEE 802.11 or Bluetooth according to IEEE 802.15.1. In LTE-LAA, a primary component carrier in the licensed spectrum provides a main connection, inter aka for control signaling, while one or more secondary component carriers are set up in the unlicensed spectrum to boost data throughput in a best-effort fashion.
While LTE achieves cell densification and delivers services with predictable quality and highest spectral efficiency, most of the available unlicensed frequency bands are used by multiple WLANs with unpredictable spatial and temporal granularity. A multitude of frequency bands is available in the unlicensed spectrum, for example starting at 5 GHz, which can be used for LTE transmission, if a suitable coexistence protocol is used. Collisions in the unlicensed spectrum between the two radio access technologies would significantly reduce the performance of both LTE and WLAN, if no coexistence measures were taken.
Furthermore, standalone LTE in the unlicensed spectrum (i.e., LTE operation without assistance in the licensed spectrum) is discussed for 3GPP LTE Release 14 and beyond as LTE-Unlicensed (LTE-U), and further as “Multefire” at the Multefire Alliance.
In each of above exemplary scenarios, at least one LTE carrier in the unlicensed spectrum shares its radio frequency spectrum with another RAT, e.g., WLAN, Bluetooth and/or an LTE carrier component of another operator. However, a transceiver adapted to perform scheduled operations within a rigid frame structure, such as an LTE transceiver, is not necessarily optimized for performing unscheduled coexistence measures.